1. Field of the Invention
The present invention relates to an image forming apparatus. More particularly, the present invention relates to an improved developing unit for use in an image forming apparatus capable of developing an image by attaching a developer directly to an electrostatic latent image formed on an image carrying medium. The invention is also directed to an image forming apparatus including the developing unit.
2. Description of the Related Art
Conventional image forming apparatuses such as a laser printer, a laser emitting diode (LED) printer, a digital copier, and a general paper facsimile, perform the printing function by transferring an image signal in accordance with an input digital signal onto a printing medium in the form of a visible image.
Such image forming apparatuses include the image carrying medium, a developing unit, a laser scanning unit, and a fixing unit.
The image carrying medium is rotatably mounted in a main body of the image forming apparatus. An electrostatic latent image is formed on a surface of the image carrying medium by a laser beam projected from the laser scanning unit. The electrostatic latent image is visualized by toner supplied through the developing unit. Generally, the toner used herein has a predetermined color and electric property. The fixing unit fuses on the printing medium the visible toner image formed on the image carrying medium which is then transferred onto the printing medium by applying heat and pressure.
The developing unit comprises a developing unit body, a developing roller mounted in the developing unit body to supply the toner to the image carrying medium, a toner supplying roller, and an auger. The developing roller applies the toner supplied into the developing unit body to the electrostatic latent image by a predetermined thickness. Control of the toner thickness is provided by the developing unit body having a doctor blade for controlling the thickness of the toner layer supplied to the surface of the developing roller. The toner supplying roller and the auger supply the developing roller with the toner supplied to the developing unit body.
The above-structured developing unit is usually provided as a separate part from the image carrying medium and therefore has a relatively long lifespan since it can be used until the developing roller expires. Accordingly, a detachable toner cartridge has been suggested to refill the toner by replacing the toner cartridge. The auger and the toner supplying roller continuously supply the toner from the toner cartridge to the developing roller.
In the above-structured developing unit, however, a dedicated support member is required for mounting of the doctor blade to the developing unit body, thereby increasing the whole size of the developing unit.
In addition, in the conventional developing unit as described above, the toner may not be evenly supplied along the length of the developing roller. The toner can be concentrated and condensed at both ends of the toner supplying roller. When the condensed toner is supplied to the image carrying medium, quality of a finally printed image deteriorates.